Synthesis and Functionalization of Highly Monodispersed Iron and Core/Iron Oxide Shell Magnetic Particles With Broadly Tunable Diameter

ABSTRACT

Provided are methods for preparing iron nanoparticles and to iron nanoparticles produced by those methods. The invention also provides methods for coating the iron nanoparticles with oxides and functionalizing the iron nanoparticles with organic and polymeric ligands. Additionally, the invention provides methods of using such iron nanoparticles.

BACKGROUND OF THE INVENTION Field of the Invention

Provided are methods for preparing iron nanoparticles and to ironnanoparticles produced by those methods. The invention also providesmethods for coating the iron nanoparticles with oxides andfunctionalizing the iron nanoparticles with organic and polymericligands. Additionally, the invention provides methods of using such ironnanoparticles.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a process for the preparation of ironnanoparticles, comprising reacting a Fe²⁺ salt with a reducing agent inthe presence of a polymer surfactant and a base.

In some embodiments, the Fe²⁺ salt is FeCl₂, FeBr₂, FeI₂, or Fe(SO₄)₂.

In some embodiments, the reducing agent is NaBH₄, LiBH₄, N₂H₄, NaH₂PO₃,NaBH₃CN, NaBH(OAc)₃, a sulfite, or an amino acid.

In some embodiments, the polymer surfactant is polyvinylpyrrolidone(PVP), polyacrylic acid, polystyrene sulfonate, poly(allylaminehydrochloride), polyvinyl alcohol, poly(methacrylic acid), polyasparticacid, polyallylamine hydrochloride,poly(2-acrylamido-2-methyl-1-propanesulfonic acid), polyacrylamide,polypeptides, glycosaminoglycans, Triton X-100, polyethylene glycolnonyl phenyl ether, or a deoxyribonucleic acid.

In some embodiments, the polymer surfactant is a PVP having a numberaverage molecular weight of 1 to 80 kilodaltons. In one embodiment, thePVP has a number average molecular weight of about 40 kilodaltons.

In some embodiments, the base is aqueous NaOH or KOH.

In some embodiments, the reducing agent and base is added to the Fe²⁺salt and the polymer surfactant over 15 minutes to 24 hours in a batchprocess.

In some embodiments, the reducing agent and base is added to the Fe²⁺salt and the polymer surfactant with stirring. In some embodiments, thestirring rate is between 50 and 2000 rpm. In some embodiments, thestirring rate is greater than 500 rpm.

In some embodiments, the reducing agent and base is added to the Fe²⁺salt and the polymer surfactant in a continuous process.

In some embodiments, the reacting is carried out in aqueous solution.

In some embodiments, the concentration of polymer surfactant in water is0.001 to 0.100 g/mL, the concentration of reducing agent is 0.01 to 1.0M, and the concentration of base is 0.0001 to 1.0 M.

In one embodiment, the polymer surfactant is PVP of 40 kilodaltonshaving a concentration of about 0.03 g/mL, the reducing agent is NaBH₄having a concentration of about 0.1M and the base is NaOH having aconcentration of about 0.6 mM to about 1.3 mM.

In some embodiments, the iron nanoparticles have an average size of50-1000 nm.

In some embodiments, the iron nanoparticles have an average size ofabout 210 nm, about 311 nm, about 400 nm, about 466 nm, about 530 nm,about 656 nm, or about 724 nm.

In some embodiments, the process further comprises isolating the ironnanoparticles.

In some embodiments, the iron nanoparticles are in the form of aprecipitate.

In some embodiments, the iron nanoparticles are dispersed in an aqueoussolution or ethanol and the aqueous solution is removed by decanting,centrifugation or filtration to give isolated iron nanoparticles.

In some embodiments, the isolated iron nanoparticles are washed with analcohol or alternatively with alcohol and water. In one embodiment, thealcohol is ethanol.

In some embodiments, the iron nanoparticles further comprise a ligand onthe iron nanoparticles.

In some embodiments, the ligand is an acrylate or a polymer.

In some embodiments, the iron nanoparticles further comprises at leastone shell on the nanoparticles. In some embodiments, the at least oneshell comprises a metal oxide. In one embodiment, the at least one shellcomprises silica.

In some embodiments, the iron nanoparticles are embedded in a polymericmatrix.

In one embodiment, the polymeric matrix comprises a polyacrylate.

In some embodiment, the iron nanoparticles are linked to a drug.

In some embodiments, provided is a method of treating a condition thatresponds to a drug, comprising administering an effective amount of theiron nanoparticles linked to the drug.

In some embodiments, the iron nanoparticles are part of a dentalrestoration.

In some embodiment, provided is a method of treating a condition thatbenefits from hyperthermia, comprising administering to an animal inneed thereof the iron nanoparticles, exposing a portion of the animal toa magnetic field, thereby concentrating the iron nanoparticles to theportion exposed to the magnetic field, and exposing the portion of theanimal to an excitation source, thereby exciting the iron nanoparticlesand causing localized hyperthermia. In one embodiment, the condition isa tumor and the portion of the animal exposed to the magnetic fieldcomprises the tumor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a scheme for a batch process for the preparation of ironnanoparticles.

FIGS. 2A, 2C and 2E show a series of SEM images of the ironnanoparticles obtained under different reaction conditions at differentconcentrations of NaOH: NaOH 1.25 mM (FIGS. 2A and 2E); and NaOH 0.625mM (FIG. 2C). FIGS. 2B, 2D, and 2F show a series of size distributioncharts of the iron nanoparticles obtained under different reactionconditions at different concentrations of NaOH: NaOH 1.25 mM (FIGS. 2Band 2F); and NaOH 0.625 mM (FIG. 2D).

FIGS. 3A-3D show a series of SEM images of iron nanoparticles withdifferent sizes: 724 nm (FIG. 3A), 656 nm (FIG. 3B), 466 nm (FIG. 3C),and 311 nm (FIG. 3D).

FIGS. 4A-4D are a series of bar graphs of size distribution of the ironnanoparticles with different sizes: 724 nm (FIG. 4A), 656 nm (FIG. 4B),466 nm (FIG. 4C), and 311 nm (FIG. 4D).

FIGS. 5A-5B are line graphs showing the intensity versus 2 Theta)(° ofthe X-ray powder diffraction (XRD) pattern of iron nanoparticles withdifferent sizes before (FIG. 5A) and after (FIG. 5B) annealing at 600°C. for 3 hours under N₂ environment.

FIG. 6 is a line graph showing differential scanning calorimetry (DSC)curves of iron nanoparticles with different sizes.

FIGS. 7A-7D are line graphs showing hysteresis loops of ironnanoparticles with different sizes at temperature of 2K and 300K under afield of 30000 Oe. The inset is a graph showing M-H loops for the samenanoparticle but under a field of 800 Oe.

FIGS. 8A-8B are photographs of the iron nanoparticles: FIG. 8A before;and FIG. 8B after being placed in the presence of a magnet.

FIG. 9 depicts a schematic illustration of a representative ironnanoparticle coated with silica and bonding ligands.

FIGS. 10A-10B are SEM images of iron nanoparticles before (FIG. 10A) andafter (FIG. 10B) coating with a silica shell.

FIGS. 11A-11F are SEM images of iron nanoparticles with a size of about300 nm after coating with a silica shell.

FIG. 12 is a TEM image of an iron nanoparticle coated with a thin layerof silica shell before removing silica nanoparticles (by-product) bymagnetic separation.

FIG. 13 is a line graph showing the transmittance (%) versus wavenumber(cm⁻¹) of the Fourier transform infrared spectroscopy (FT-IR) spectra ofiron nanoparticles coated with a thin layer of silica andsurface-functionalized with functional groups of polymerizableacrylates: (A) Fe; (B) Fe core with SiO₂ shell nanoparticles; (C) Fecore with SiO₂ shell nanoparticles functionalized with acrylate group(3-mercaptopropyl trimethoxysilane (KH570, 95%)) on the surface.

FIG. 14 is a scheme for a continuous synthesis process of ironnanoparticles in a flow tubing reactor.

FIG. 15 is a photograph of simple setup for the continuous synthesisprocess of iron nanoparticles in a flow tubing reactor.

FIGS. 16A-16B are SEM images of iron nanoparticles with different sizes:250 nm (FIG. 16A), and 500 nm (FIG. 16B).

FIG. 17A is a bar graph showing Degree of Conversion of ironnanoparticle-doped adhesive resins with different nanoparticle sizes andconcentrations compared to the control (adhesives with nonanoparticles). FIG. 17B is a line graph showing the Shrinkage Stress(MPa) versus Time (s) of iron nanoparticle-doped adhesive resins(adhesive with 5 wt % of 900 nm nanoparticle) compared to the control(adhesives with no nanoparticles).

FIGS. 18A-18D are SEM images of representative examples from teethrestored using control adhesive (FIG. 18A), iron nanoparticle-dopedadhesive resin with no magnetic pull (FIG. 18B), iron nanoparticle-dopedadhesive resin with a 60 second magnetic pull (FIG. 18C), and anenlarged image of FIG. 18C highlighting the horizontal cross-linking(white arrows) (FIG. 18D). Density of resin tags formed by the ironnanoparticle-doped adhesive resin suggested superior infiltration (FIG.18D).

FIG. 19A is a bar graph showing quantification of average resin taglength. FIG. 19B is a bar graph showing quantification of average resintag density. FIG. 19C is a bar graph showing shear bond strength ofteeth restored using the nanoparticle-doped adhesive system compared tothat using the controls.

FIG. 20A is a bar graph showing detected tumor necrosis factor alpha(TNF-α) at various time points after pull of nanoparticles into pulp.FIG. 20B is a bar graph showing detected transforming growth factoralpha (TGF-α) at various time points after pull of nanoparticles intopulp. No significant differences were detected in TNF-α (FIG. 20A,p=0.65) and TGF-α (FIG. 20B, p=0.78) in rat molar pulp tissue at varioustime points after pull of nanoparticles into pulp. Control:nanoparticles without magnetic pull, Experimental: nanoparticles withmagnetic pull.

DETAILED DESCRIPTION OF THE INVENTION

The invention described herein are highly monodispersed iron and ironcore/iron oxide shell magnetic particles with broadly tunable diameters(50-1000 nm range) and methods of making the same.

In one embodiments, provided is a process for the preparation of ironnanoparticles, comprising reacting a Fe²⁺ salt with a reducing agent inthe presence of a polymer surfactant and a base.

We have developed i) a synthetic method for the preparation of highlymonodispersed iron and iron core/iron oxide shell magnetic particlesthrough batch reaction and/or continuous microfluidic reaction, ii) astrategy for controlling the color of the magnetic particles, and iii) aprotocol for the functionalization of such magnetic particles withpolymerizable acrylate ligands. This approach is based on the fastreduction of iron ions in the presence of FDA-approved polymersurfactants. This method has the following unique merits: i) it allowsfor the precise control over the diameter of the particles in a range of50-1000 nm; ii) It is scalable to produce large quantity of particles;iii) It is simple yet reproducible; iv) It is compatible with continuoussynthesis in flow; and v) the particles are biocompatible. We furtherdeveloped a synthetic route for the surface modification of magneticparticles with acrylate monomers. The acrylate-functionalized magneticparticles can be used for new generation of dental materials.

Due to their large magnetization and magnetostatic force, pure Feparticles have been widely used in magnetism and electricity, catalysis,labeling and magnetic separation of biological materials, MM contrastenhancement, hyperthermia treatment and drug delivery^([1,2]). Theproperties of Fe particles are strongly dependent on their size andshape. There is a burgeoning literature about the synthesis of small Fenanoparticles with diameter below about 20 nm using the thermaldecomposition of iron pentacarbonyl^([2, 3]). However, there are onlyfew reports on the preparation of monodispersed Fe particles over 100nm. Three major methods are: (1) gas flow sputtering^([1]), (2)reduction of Fe₂O₃ or Fe₃O₄ by heating under CO or H₂atmosphere^([4-6]), and (3) chemical reduction by NaBH₄ ^([7, 8]).However, the methods (1) and (2) are not cost-effective, and they offerlimited control over the size and size distribution of particles. Themethod (3) mainly produces Fe particle chains. To date, there is noreport on the synthesis of highly monodispersed spherical Fenanoparticles with tunable diameter. Therefore, there is urgent todevelop a simple, scalable yet inexpensive strategy for the synthesismethod of Fe nanoparticles. We have recently developed i) a syntheticmethod for the preparation of highly monodispersed iron and ironcore/iron oxide shell magnetic particles through batch reaction and/orcontinuous microfluidic reaction, ii) a strategy for controlling thecolor of the magnetic particles, and iii) a protocol for thefunctionalization of such magnetic particles with polymerizable acrylateligands. The synthetic approach is based on the fast reduction of Fe²⁺ions in the presence of FDA-approved polymer surfactant(polyvinylpyrrolidone, PVP). This method has the following uniquemerits: i) it allows for the precise control over the diameter of theparticles in a range of 50-1000 nm; ii) it is scalable to produce largequantity of particles; iii) it is simple yet reproducible; iv) it iscompatible with continuous synthesis in flow; and v) the particles arebiocompatible. We further developed a synthetic route for the surfacemodification of magnetic particles with acrylate monomers. Theacrylate-functionalized magnetic particles can be used for newgeneration of dental materials.

Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention pertains. The following definitionssupplement those in the art and are directed to the current applicationand are not to be imputed to any related or unrelated case, e.g., to anycommonly owned patent or application. Although any methods and materialssimilar or equivalent to those described herein can be used in thepractice for testing of the present invention, the preferred materialsand methods are described herein. Accordingly, the terminology usedherein is for the purpose of describing particular embodiments only, andis not intended to be limiting.

As used in this specification and the appended claims, the singularforms “a,” “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “ananoparticle” includes a plurality of such nanoparticles, and the like.

The term “about,” as used herein, includes the recited number±10%. Forexample, “about 100 nm” encompasses a range of sizes from 90 nm to 110nm.

The term “nanoparticles” as used herein refers to solid particles havinga size of less than 1000 nm.

As used herein, the term “shell” refers to material deposited onto ananoparticle core or onto previously deposited shells of the same ordifferent composition and that result from a single act of deposition ofthe shell material.

A “ligand” is a molecule capable of interacting (whether weakly orstrongly) with one or more faces of a nanostructure, e.g., throughcovalent, ionic, van der Waals, or other molecular interactions with thesurface of the nanostructure.

Unless clearly indicated otherwise, ranges listed herein are inclusive.

A variety of additional terms are defined or otherwise characterizedherein.

Process for Synthesizing Iron Nanoparticles

Provided is a process to prepare iron nanoparticles, comprising reactinga Fe²⁺ salt with a reducing agent in the presence of a polymersurfactant and a base. In one embodiment, the Fe²⁺ salt is FeCl₂, thereducing agent is NaBH₄, and the polymer surfactant ispolyvinylpyrrolidone (PVP).

In some embodiments, the Fe²⁺ salt is FeCl₂, FeBr₂, FeI₂, or Fe(SO₄)₂.In some embodiments, the Fe²⁺ salt is FeCl₂.

In some embodiments, the reducing agents is NaBH₄, LiBH₄, N₂H₄, NaH₂PO,NaBH₃CN, NaBH(OAc)₃, a sulfite, or an amino acid. Examples of aminoacids that may be used as a reducing agent include methionine andcysteine. Examples of sulfites that may be used as a reducing agentinclude sodium sulfite, sodium hydrogen sulfite, sodium metabisulfite,potassium metabisulfite, potassium sulfite, calcium sulfite, calciumhydrogen sulfite, potassium hydrogen sulfite. In some embodiments, thereducing agent is NaBH₄.

In some embodiments, the concentration of the reducing agent is about0.01 M to 0.05 M, 0.01 M to 0.10 M, 0.01 M to 0.20 M, 0.01 M to 0.30 M,0.01 M to 0.40 M, 0.01 M to 0.50 M, 0.01 M to 0.60 M, 0.01 M to 0.70 M,0.01 M to 0.80 M, 0.01 M to 0.90 M, 0.01 M to 1.00 M, 0.05 M to 0.10 M,0.05 M to 0.20 M, 0.05 M to 0.30 M, 0.05 M to 0.40 M, 0.05 M to 0.50 M,0.05 M to 0.60 M, 0.05 M to 0.70 M, 0.05 M to 0.80 M, 0.05 M to 0.90 M,0.05 M to 1.00 M, 0.10 M to 0.20 M, 0.10 M to 0.30 M, 0.10 M to 0.40 M,0.10 M to 0.50 M, 0.10 M to 0.60 M, 0.10 M to 0.70 M, 0.10 M to 0.80 M,0.10 M to 0.90 M, 0.10 M to 1.00 M, 0.20 M to 0.30 M, 0.20 M to 0.40 M,0.20 M to 0.50 M, 0.20 M to 0.60 M, 0.20 M to 0.70 M, 0.20 M to 0.80 M,0.20 M to 0.90 M, 0.20 M to 1.00 M, 0.30 M to 0.40 M, 0.30 M to 0.50 M,0.30 M to 0.60 M, 0.30 M to 0.70 M, 0.30 M to 0.80 M, 0.30 M to 0.90 M,0.30 M to 1.00 M, 0.40 M to 0.50 M, 0.40 M to 0.60 M, 0.40 M to 0.70 M,0.40 M to 0.80 M, 0.40 M to 0.90 M, or 0.40 M to 1.00 M.

In some embodiments, the polymer surfactant is polyvinylpyrrolidone(PVP), polyacrylic acid, polystyrene sulfonate, poly(allylaminehydrochloride), polyvinyl alcohol, poly(methacrylic acid), polyasparticacid, polyallylamine hydrochloride,poly(2-acrylamido-2-methyl-1-propanesulfonic acid), polyacrylamide,polypeptides, glycosaminoglycans, Triton X-100, polyethylene glycolnonyl phenyl ether, or a deoxyribonucleic acid. In some embodiments, thepolymer surfactant is PVP.

In some embodiments, the number average molecular weight of PVP is 1kilodalton to 5 kilodaltons, 1 kilodaltons to 10 kilodaltons, 1kilodaltons to 20 kilodaltons, 1 kilodaltons to 30 kilodaltons, 1kilodaltons to 40 kilodaltons, 1 kilodaltons to 50 kilodaltons, 1kilodaltons to 60 kilodaltons, 1 kilodaltons to 70 kilodaltons, 1kilodaltons to 80 kilodaltons, 1 kilodaltons to 90 kilodaltons, 1kilodaltons to 100 kilodaltons, 5 kilodaltons to 10 kilodaltons, 5kilodaltons to 20 kilodaltons, 5 kilodaltons to 30 kilodaltons, 5kilodaltons to 40 kilodaltons, 5 kilodaltons to 50 kilodaltons, 5kilodaltons to 60 kilodaltons, 5 kilodaltons to 70 kilodaltons, 5kilodaltons to 80 kilodaltons, 5 kilodaltons to 90 kilodaltons, 5kilodaltons to 100 kilodaltons, 10 kilodaltons to 20 kilodaltons, 10kilodaltons to 30 kilodaltons, 10 kilodaltons to 40 kilodaltons, 10kilodaltons to 50 kilodaltons, 10 kilodaltons to 60 kilodaltons, 10kilodaltons to 70 kilodaltons, 10 kilodaltons to 80 kilodaltons, 10kilodaltons to 90 kilodaltons, 10 kilodaltons to 100 kilodaltons, 20kilodaltons to 30 kilodaltons, 20 kilodaltons to 40 kilodaltons, 20kilodaltons to 50 kilodaltons, 20 kilodaltons to 60 kilodaltons, 20kilodaltons to 70 kilodaltons, 20 kilodaltons to 80 kilodaltons, 20kilodaltons to 90 kilodaltons, 20 kilodaltons to 100 kilodaltons, 30kilodaltons to 40 kilodaltons, 30 kilodaltons to 50 kilodaltons, 30kilodaltons to 60 kilodaltons, 30 kilodaltons to 70 kilodaltons, 30kilodaltons to 80 kilodaltons, 30 kilodaltons to 90 kilodaltons, 30kilodaltons to 100 kilodaltons, 40 kilodaltons to 50 kilodaltons, 40kilodaltons to 60 kilodaltons, 40 kilodaltons to 70 kilodaltons, 40kilodaltons to 80 kilodaltons, 40 kilodaltons to 90 kilodaltons, or 40kilodaltons to 100 kilodaltons. In some embodiments, the number averagemolecular weight of PVP is 1 kilodalton to 80 kilodaltons.

In some embodiments, the number average molecular weight (kilodaltons)of PVP is about 1 kilodalton, about 5 kilodaltons, about 10 kilodaltons,about 20 kilodaltons, about 30 kilodaltons, about 40 kilodaltons, about50 kilodaltons, about 60 kilodaltons, about 70 kilodaltons, about 80kilodaltons, about 90 kilodaltons or about 100 kilodaltons. In someembodiments, the number average molecular weight (kilodaltons) of PVP isabout 40 kilodaltons.

In some embodiments, the concentration of the PVP in water is 0.001 g/mLto 0.005 g/mL, 0.001 g/mL to 0.010 g/mL, 0.001 g/mL to 0.020 g/mL, 0.001g/mL to 0.030 g/mL, 0.001 g/mL to 0.040 g/mL, 0.001 g/mL to 0.050 g/mL,0.001 g/mL to 0.060 g/mL, 0.001 g/mL to 0.070 g/mL, 0.001 g/mL to 0.080g/mL, 0.001 g/mL to 0.090 g/mL, 0.001 g/mL to 0.100 g/mL, 0.005 g/mL to0.010 g/mL, 0.005 g/mL to 0.020 g/mL, 0.005 g/mL to 0.030 g/mL, 0.005g/mL to 0.040 g/mL, 0.005 g/mL to 0.050 g/mL, 0.005 g/mL to 0.060 g/mL,0.005 g/mL to 0.070 g/mL, 0.005 g/mL to 0.080 g/mL, 0.005 g/mL to 0.090g/mL, 0.005 g/mL to 0.100 g/mL, 0.010 g/mL to 0.020 g/mL, 0.010 g/mL to0.030 g/mL, 0.010 g/mL to 0.040 g/mL, 0.010 g/mL to 0.050 g/mL, 0.010g/mL to 0.060 g/mL, 0.010 g/mL to 0.070 g/mL, 0.010 g/mL to 0.080 g/mL,0.010 g/mL to 0.090 g/mL, 0.010 g/mL to 0.100 g/mL, 0.020 g/mL to 0.030g/mL, 0.020 g/mL to 0.040 g/mL, 0.020 g/mL to 0.050 g/mL, 0.020 g/mL to0.060 g/mL, 0.020 g/mL to 70.00 g/mL, 0.020 g/mL to 0.080 g/mL, 0.020g/mL to 0.090 g/mL, 0.020 g/mL to 0.100 g/mL, 0.030 g/mL to 0.040 g/mL,0.030 g/mL to 0.050 g/mL, 0.030 g/mL to 0.060 g/mL, 0.030 g/mL to 0.070g/mL, 0.030 g/mL to 0.080 g/mL, 0.030 g/mL to 0.090 g/mL, 0.030 g/mL to0.100 g/mL, 0.040 g/mL to 0.050 g/mL, 0.040 g/mL to 0.060 g/mL, 0.040g/mL to 0.070 g/mL, 0.040 g/mL to 0.080 g/mL, 0.040 g/mL to 0.090 g/mL,or 0.040 g/mL to 0.100 g/mL.

Exemplary PVPs include those sold under the name PVP10 (Sigma-Aldrich),PVP40 (Sigma-Aldrich), PVP360 (Sigma-Aldrich), and under the trade nameLUVITEC® (BASF Corporation), LUVICROSS® (BASF Corporation), COLLACRAL®VAL (BASF Corporation), Plasdone™ (Ashland Global Holdings Inc.),Kollidon® 25, Kollidon® 30 and Kollidon® 90 (BASF Corporation).

In some embodiments, the base is aqueous NaOH or KOH. In someembodiments, the base is NaOH.

In some embodiments, the concentration of the base is about 0.01 M to0.05 M, 0.01 M to 0.10 M, 0.01 M to 0.20 M, 0.01 M to 0.30 M, 0.01 M to0.40 M, 0.01 M to 0.50 M, 0.01 M to 0.60 M, 0.01 M to 0.70 M, 0.01 M to0.80 M, 0.01 M to 0.90 M, 0.01 M to 1.00 M, 0.05 M to 0.10 M, 0.05 M to0.20 M, 0.05 M to 0.30 M, 0.05 M to 0.40 M, 0.05 M to 0.50 M, 0.05 M to0.60 M, 0.05 M to 0.70 M, 0.05 M to 0.80 M, 0.05 M to 0.90 M, 0.05 M to1.00 M, 0.10 M to 0.20 M, 0.10 M to 0.30 M, 0.10 M to 0.40 M, 0.10 M to0.50 M, 0.10 M to 0.60 M, 0.10 M to 0.70 M, 0.10 M to 0.80 M, 0.10 M to0.90 M, 0.10 M to 1.00 M, 0.20 M to 0.30 M, 0.20 M to 0.40 M, 0.20 M to0.50 M, 0.20 M to 0.60 M, 0.20 M to 0.70 M, 0.20 M to 0.80 M, 0.20 M to0.90 M, 0.20 M to 1.00 M, 0.30 M to 0.40 M, 0.30 M to 0.50 M, 0.30 M to0.60 M, 0.30 M to 0.70 M, 0.30 M to 0.80 M, 0.30 M to 0.90 M, 0.30 M to1.00 M, 0.40 M to 0.50 M, 0.40 M to 0.60 M, 0.40 M to 0.70 M, 0.40 M to0.80 M, 0.40 M to 0.90 M, or 0.40 M to 1.00 M.

In some embodiments, the concentration of NaOH or KOH is about 0.1 mM toabout 0.2 mM, 0.1 mM to about 0.3 mM, 0.1 mM to about 0.4 mM, 0.1 mM toabout 0.5 mM, 0.1 mM to about 0.6 mM, 0.1 mM to about 0.7 mM, 0.1 mM toabout 0.8 mM, 0.1 mM to about 0.9 mM, 0.1 mM to about 1.0 mM, 0.1 mM toabout 1.1 mM, 0.1 mM to about 1.2 mM, 0.1 mM to about 1.3 mM, 0.1 mM toabout 1.4 mM, 0.1 mM to about 1.5 mM, 0.2 mM to about 0.3 mM, 0.2 mM toabout 0.4 mM, 0.2 mM to about 0.5 mM, 0.2 mM to about 0.6 mM, 0.2 mM toabout 0.7 mM, 0.2 mM to about 0.8 mM, 0.2 mM to about 0.9 mM, 0.2 mM toabout 1.0 mM, 0.2 mM to about 1.1 mM, 0.2 mM to about 1.2 mM, 0.2 mM toabout 1.3 mM, 0.2 mM to about 1.4 mM, 0.2 mM to about 1.5 mM, 0.3 mM toabout 0.4 mM, 0.3 mM to about 0.5 mM, 0.3 mM to about 0.6 mM, 0.3 mM toabout 0.7 mM, 0.3 mM to about 0.8 mM, 0.3 mM to about 0.9 mM, 0.3 mM toabout 1.0 mM, 0.3 mM to about 1.1 mM, 0.3 mM to about 1.2 mM, 0.3 mM toabout 1.3 mM, 0.3 mM to about 1.4 mM, 0.3 mM to about 1.5 mM, 0.4 mM toabout 0.5 mM, 0.4 mM to about 0.6 mM, 0.4 mM to about 0.7 mM, 0.4 mM toabout 0.8 mM, 0.4 mM to about 0.9 mM, 0.4 mM to about 1.0 mM, 0.4 mM toabout 1.1 mM, 0.4 mM to about 1.2 mM, 0.4 mM to about 1.3 mM, 0.4 mM toabout 1.4 mM, 0.4 mM to about 1.5 mM, 0.5 mM to about 0.6 mM, 0.5 mM toabout 0.7 mM, 0.5 mM to about 0.8 mM, 0.5 mM to about 0.9 mM, 0.5 mM toabout 1.0 mM, 0.5 mM to about 1.1 mM, 0.5 mM to about 1.2 mM, 0.5 mM toabout 1.3 mM, 0.5 mM to about 1.4 mM, 0.5 mM to about 1.5 mM, 0.6 mM toabout 0.7 mM, 0.6 mM to about 0.8 mM, 0.6 mM to about 0.9 mM, 0.6 mM toabout 1.0 mM, 0.6 mM to about 1.1 mM, 0.6 mM to about 1.2 mM, 0.6 mM toabout 1.3 mM, 0.6 mM to about 1.4 mM, 0.6 mM to about 1.5 mM, 0.7 mM toabout 0.8 mM, 0.7 mM to about 0.9 mM, 0.7 mM to about 1.0 mM, 0.7 mM toabout 1.1 mM, 0.7 mM to about 1.2 mM, 0.7 mM to about 1.3 mM, 0.7 mM toabout 1.4 mM, 0.7 mM to about 1.5 mM.

In some embodiments, the concentration of NaOH or KOH is about 0.1 mM,about 0.2 mM, about 0.3 mM, about 0.4 mM, about 0.5 mM, about 0.6 mM,about 0.7 mM, about 0.8 mM, about 0.9 mM, about 1.0 mM, about 1.1 mM,about 1.2 mM, about 1.3 mM, about 1.4 mM, or about 1.5 mM.

In some embodiments, the reducing agent and the base are added to theFe²⁺ salt and the polymer surfactant over 15 minutes to 24 hours, over15 minutes to 20 hours, over 15 minutes to 15 hours, over 15 minutes to10 hours, over 15 minutes to 5 hours, over 15 minutes to 1 hour, over 15minutes to 30 minutes, over 30 minutes to 24 hours, over 30 minutes to20 hours, over 30 minutes to 15 hours, over 30 minutes to 10 hours, over30 minutes to 5 hours, over 30 minutes to 1 hour, over 1 hour to 24hours, over 1 hour to 20 hours, over 1 hour to 15 hours, over 1 hour to10 hours, over 1 hour to 5 hours, over 5 hours to 24 hours, over 5 hoursto 20 hours, over 5 hours to 15 hours, over 5 hours to 10 hours, over 10hours to 24 hours, over 10 hours to 20 hours, over 10 hours to 15 hours,over 15 hours to 24 hours, over 15 hours to 20 hours, or over 20 hoursto 24 hours.

In one embodiment, the reducing agent and the base is added to the Fe²⁺salt and polymer surfactant with stirring in a batch process as depictedin FIG. 1.

In some embodiments, the stirring rate is between 50 rpm and 2,000 rpm,between 50 rpm and 1,750 rpm, between 50 rpm and 1,500 rpm, between 50rpm and 1,250 rpm, between 50 rpm and 1,000 rpm, between 50 rpm and 750rpm, between 50 rpm and 500 rpm, between 50 rpm and 100 rpm, between 100rpm and 2,000 rpm, between 100 rpm and 1,750 rpm, between 100 rpm and1,500 rpm, between 100 rpm and 1,250 rpm, between 100 rpm and 1,000 rpm,between 100 rpm and 750 rpm, between 100 rpm and 500 rpm, between 500rpm and 2,000 rpm, between 500 rpm and 1,750 rpm, between 500 rpm and1,500 rpm, between 500 rpm and 1,250 rpm, between 500 rpm and 1,000 rpm,between 500 rpm and 750 rpm, between 750 rpm and 2,000 rpm, between 750rpm and 1,750 rpm, between 750 rpm and 1,500 rpm, between 750 rpm and1,250 rpm, between 750 rpm and 1,000 rpm, between 1,000 rpm and 2,000rpm, between 1000 rpm and 1,750 rpm, between 1,000 rpm and 1,500 rpm,between 1,000 rpm and 1,250 rpm, between 1,250 rpm and 2,000 rpm,between 1,250 rpm and 1,750 rpm, between 1,250 rpm and 1,500 rpm,between 1,500 rpm and 2,000 rpm, or between 1,500 rpm and 1,750 rpm.

In some embodiments, the stirring rate is greater than 500 rpm.

In some embodiments, the reducing agent and the base is added to theFe²⁺ salt and the polymer surfactant in a continuous process. In oneembodiment, a mixture of the reducing agent and the base is filled in asyringe. The mixture solution is slowly introduced into the reactionsystem by using a syringe pump. In another embodiment, two syringes thatcontain the reducing agent and the base separately are used forcontinuous injection of reactants.

In some embodiments, the process comprises using a continuousmicroreactor to synthesize the magnetic nanoparticles. In oneembodiment, a mixture of reducing agents is filled in one syringe; and amixture of Fe²⁺ salt and polymer surfactant is filled in anothersyringe. Then the two liquids are simultaneously injected into a channelor a tubing and mixed in the channel or the tubing to react. The finalproduct is collected at the end of the channel or the tubing.

In some embodiments, the sizes of iron nanoparticles are tuned bycontrolling the concentration and ratio of chemicals, for example, base,reducing agent, and polymer surfactant, and the additional rate ofchemicals. In some embodiments, the sizes of iron nanoparticles aretuned by controlling the concentration of base, e.g., NaOH or KOH. Thesize of iron nanoparticles increases with a decrease of theconcentration of NaOH.

In some embodiments, the sizes of iron nanoparticles are tuned bychanging the solvent of the reaction, e.g., using water or ethanolmixture as solvent.

The size of the iron nanoparticles were determined by measuring theiraverage diameter.

In some embodiments, the nanoparticles have an average diameter of 1000nanometers or less. In some embodiments, the iron nanoparticles may havean average diameter of 1000 nanometers or less. In some embodiments, thediameter of the nanoparticle is between about 50 nm and about 1000 nm,between about 50 nm and about 800 nm, between about 50 nm and about 600nm, between about 50 nm and about 400 nm, between about 50 nm and about200 nm, between about 50 nm and about 100 nm, between about 100 nm andabout 1000 nm, between about 100 nm and about 800 nm, between about 100nm and about 600 nm, between about 100 nm and about 400 nm, betweenabout 100 nm and about 200 nm, between about 200 nm and about 1000 nm,between about 200 nm and about 800 nm, between about 200 nm and about600 nm, between about 200 nm and about 400 nm, between about 400 nm andabout 1000 nm, between about 400 nm and about 800 nm, between about 400nm and about 600 nm, between about 600 nm and about 1000 nm, betweenabout 600 nm and about 800 nm, or between about 800 nm and about 1000nm. In some embodiments, the average diameter of the nanoparticle isabout 210 nm. In some embodiments, the average diameter of thenanoparticle is about 400 nm. In some embodiments, the average diameterof the nanoparticle is about 530 nm.

In some embodiments, the iron nanoparticles are in the form of aprecipitate. In some process, the iron nanoparticles are in an aqueoussolution and the solution is removed by decanting, centrifugation orfiltration to isolate the iron nanoparticles. In another embodiment, theiron nanoparticles are concentrated by placing in the vicinity of amagnet and the solution is decanted.

In some embodiments, the iron nanoparticles are washed with a solvent.In some embodiments, the solvent is water, an alcohol, hexane, toluene,benzene, chloroform, or a mixture thereof. In one embodiment, thesolvent is ethanol.

Shells

In some embodiments, the iron nanoparticles comprise at least one shellon the iron nanoparticles. Suitable shell materials include, but are notlimited to, silica, alumina, titanium dioxide, zirconium dioxide, copperoxide, silver oxide, and the like. In some embodiments, the at least oneshell comprises a metal oxide. In one embodiment, the at least one shellcomprises iron oxide. In one embodiment, the at least one shellcomprises silica. Exemplary synthesis of metal oxide shell andcore/shell nanostructures is disclosed in U.S. Pat. Nos. 9,390,845,8,343,627, and U.S. Patent No. US20120012778 A1.

In some embodiments, the shell has a thickness in the range from about 2nm to about 100 nm, from about 2 nm to about 80 nm, from about 2 nm toabout 60 nm, from about 2 nm to about 40 nm, from about 2 nm to about 20nm, from about 2 nm to about 10 nm, from about 2 nm to about 5 nm, fromabout 5 nm to about 100 nm, from about 5 nm to about 80 nm, from about 5nm to about 60 nm, from about 5 nm to about 40 nm, from about 5 nm toabout 20 nm, from about 5 nm to about 10 nm, from about 10 nm to about100 nm, from about 10 nm to about 80 nm, from about 10 nm to about 60nm, from about 10 nm to about 40 nm, from about 10 nm to about 20 nm,from about 20 nm to about 100 nm, from about 20 nm to about 80 nm, fromabout 20 nm to about 60 nm, from about 20 nm to about 40 nm, from about40 nm to about 100 nm, from about 40 nm to about 80 nm, from about 40 nmto about 60 nm, from about 60 nm to about 100 nm, from about 60 nm toabout 80 nm, or from about 80 nm to about 100 nm.

Surface Functionalization

To modify the surface chemistry of the iron nanoparticles, a broad rangeof organic ligands with varying functional groups can be used to coatthe surface of the iron nanoparticles or through an intermediate layerof oxide(s).

Examples of organic ligands for the iron nanoparticles include, but notlimited to, alkane, alkene, alkyne, ketone, ether, nitrile, alcohol,polyol, polyethylene glycol, polypropylene glycol, amide,polyvinylpyrolidone, polyacrylate, polymethacrylate, polyacrylic acid,ester, polyester, primary amine, secondary amine, tertiary amine,polyamine, sulfate, sulfonate, sulfonic acid, phosphate, phosphonate,phosphonic acid, fluorinated compounds (e.g., perfluoropolyether,fluoroalkane, ionic fluorocompounds, polyethylene glycol functionalizedfluorocompounds), silicones, reactive silane groups (e.g.,alkoxysilane), carboxylic acid, quaternary ammonium, phosphonium,zwitterion (e.g., phosphoryl choline, amino acids, and amino-sulfonicacids based compounds), aldehyde, surfactants, peptides, and nucleicacids.

In some embodiments, the iron nanoparticles are embedded in a polymericmatrix comprising the organic ligands described above. In someembodiment, the polymeric matrix comprises a polyacrylate.

Uses

In some embodiments, the iron nanoparticles can be used for drugdelivery. In some embodiments, the iron nanoparticles are linked to awide variety of ligands, including but not limited to, antibodies,antibody fragments, peptides, small molecules, polysaccharides, nucleicacids, aptamers, peptidomimetics, other mimetics and drugs alone or incombination. The ligands may be attached covalently (direct-conjugation)or noncovalently (indirect conjugation) to the nanoparticle surface. Insome embodiments, the iron nanoparticles are linked to a drug. In someembodiments, the drug can be encapsulated in the coated structure. SeeU.S. Pat. Nos. 7,459,145 and 6,676,963 for methods of usingnanoparticles in drug delivery.

Provided is a method of treating a condition that responds to a drug,comprising administering an effective amount of the iron nanoparticleslinked to the drug.

In some embodiments, iron nanoparticles with ceramic oxide shells can beused to prepare ceramic mouldings for dental restoration. In someembodiments, the ceramic mouldings may be prepared by forming asuspension comprising iron nanoparticles with ceramic oxide shell, apolyreactive binder, an organic component, and additives; preparing agreen body by curing the suspension by local introduction of radiationenergy with formation of the geometric shape of the green body;subjecting the green body to a heat treatment to remove the binder toobtain a white body, and sintering the white body. See U.S. Patent Pub.No. US 2010/0025874 A1 for more details about preparing ceramicmouldings. In some embodiments, the ceramic oxide includes, but is notlimited to, zirconium dioxide, aluminum oxide, barium oxide, and zincoxide.

In some embodiments, provided is an adhesive resin doped with the ironnanoparticles. In some embodiments, the adhesive resin is a dentaladhesive.

In some embodiments, the iron nanoparticle can be used to treat acondition that benefits from hyperthermia. In some embodiments, thetreatment comprises administering the iron nanoparticles to an animal inneed thereof; exposing a portion of the animal to a magnetic field,thereby concentrating the iron nanoparticles to the portion exposed tothe magnetic field; and exposing the portion of the animal to anexcitation source, thereby causing excitation of the iron nanoparticlesand localized hypothermia. In some embodiments, the excitation source islight. In some embodiments, the excitation source is laser light. Theinduced localized hyperthermia can be used to repair tissue, e.g.,joining tissue with other tissue or tissue with non-tissue material. SeeU.S. Pat. No. 6,685,730 for more details about treating variousconditions involving hyperthermia treatment using nanoparticles.

In some embodiments, the condition is a tumor and the portion of theanimal exposed to the magnetic field comprises the tumor.

EXAMPLES

The following examples are illustrative and non-limiting, of theproducts and methods described herein. Suitable modifications andadaptations of the variety of conditions, formulations, and otherparameters normally encountered in the field and which are obvious tothose skilled in the art in view of this disclosure are within thespirit and scope of the invention.

Example 1 Synthesis of Iron Nanoparticles

A general method to synthesize monodispersed iron nanoparticles isdescribed here. The synthesis scheme of FIG. 1 illustrates one method.An aqueous solution of PVP and FeCl₂ is placed in a three-neck flask.After being bubbled with argon (or nitrogen gas) to remove oxygendissolved in the solution, an ice-cold aqueous solution of NaBH₄ andNaOH mixture is drop-wise added into the reaction using glass pipette(or slowly added into the reaction using syringe pump) under mechanicalstirring. After completion of the reaction, iron nanoparticles areseparated from the reaction by magnetic pulling using a magnetic bar.The iron nanoparticles are washed alternatively with water and ethanolto remove surfactants and/or unreacted precursors. The final product isstored in ethanol for future use.

General synthetic protocol for iron nanoparticles: All the chemicalswere used directly without further treatment. The iron nanoparticleswere prepared by a chemical reduction of Fe²⁺ ions in the presence ofPVP surfactant. NaBH₄ was used as the reducing agent and FeCl₂ was usedas the source of Fe. The sizes of the iron nanoparticles were tuned bycontrolling the concentration of chemicals and the additional rate ofchemicals. In a typical synthesis, a predetermined amount of FeCl₂ and 1g PVP (M_(w)=40,000) were mixed in 30 ml H₂O. A 45 mL solution of NaBH₄(0.1 M) and NaOH (1.25 mM) were added slowly into the above solutionunder vigorous mechanical stirring (>500 rpm). After the reactionproceeded for 20 minutes, the black precipitates were washed withethanol several times and kept in ethanol.

Example 2 Tuning the Sizes of Iron Nanoparticles

Materials: Iron (II) chloride tetrahydrate (≥99%), 3-mercaptopropyltrimethoxysilane (KH570, 95%), Tetraethyl orthosilicate (TEOS, ≥99%),sodium borohydride (99%), polyvinylpyrrolidone (Mw 40,000), sodiumhydroxide (≥99%), ammonium hydroxide solution (28% NH₃ in H₂O, ≥99.99%)were purchased from Aldrich and used as received. Deionized water wasused for the preparation of all the aqueous solutions.

Synthetic protocol for iron nanoparticles with controlled size: Highlymonodisperse iron nanoparticles with controlled size were prepared by achemical reduction of Fe²⁺ ions in the presence of PVP surfactant. NaBH₄was used as the reducing agent and FeCl₂ was used as the source of Fe.The sizes of iron nanoparticles were tuned by controlling theconcentration and the additional rate of chemicals or by varying thesolvent composition for the reaction such as the ratio of ethanol towater solvent for the reaction. In a typical synthesis of ironnanoparticles with a size of about 530 nm, 1.00 g polyvinylpyrrolidone(PVP, M_(w)=40,000) was added into a 30.0 ml aqueous solution of Iron(II) chloride tetrahydrate (0.025 M) in a beaker. The solution wassonicated for 15 minutes to dissolve PVP and a homogeneous solution(called Solution A) was obtained. In another beaker, a 45.0 mL ice-coldsodium borohydride (0.100 M) aqueous solution and a 0.28 ml ice-coldsodium hydroxide NaOH (0.100 M) aqueous solution were mixed to produce aSolution B (ice-cold). The Solution A was transferred into a roundbottom flask with three necks (Scheme 1). The solution was bubbled withargon (or nitrogen gas) to remove oxygen dissolved in the solution.Under vigorous mechanical stirring (560 rpm), Solution B was dropwiseadded into Solution A slowly using a glass pipette or slowly added intothe reaction using a syringe pump under mechanical stirring. Solution Bwas kept in an ice-cold bath during the addition process. Aftercompletion of the reaction, the iron nanoparticles were separated fromthe reaction by magnetic pulling using a magnetic bar. The ironnanoparticles were washed alternatively with water and ethanol to removesurfactants and/or unreacted precursors. The precipitates were washedwith ethanol for 5 times to remove PVP and the iron nanoparticles werestored in ethanol for further use.

FIGS. 2A, 2C, and 2E show representative SEM images of these productsobtained at different concentrations of NaOH and addition rate ofprecursors. FIGS. 2B, 2D, and 2F show the representative sizedistributions of these products obtained at different concentrations ofNaOH and addition rate of precursors. All the three samples containedmagnetic particles with uniform sizes. When the concentration of NaOHwas 1.25 mM, iron nanoparticles with an average diameter of 215±27 nmwere produced (FIG. 2A and FIG. 2B). The size of iron nanoparticlesincreased with the decrease in the concentration of NaOH. Ironnanoparticles with an average size of 535±25 nm were synthesized whenthe concentration of NaOH was reduced to 0.625 mM (FIG. 2C and FIG. 2D).The quality of iron nanoparticles was further improved by controllingthe addition rate of reductant. As shown in FIG. 2E and FIG. 2F, themorphology of iron nanoparticles (˜400±23 nm in diameter) was furtherenhanced when the addition rate of reductant was optimized. This can beascribed to the control over the nucleation rate of iron nanoparticlesat the initial stage.

FIGS. 3A-3D shows representative SEM images of iron nanoparticles withdifferent nanoparticle sizes obtained at different ratios of ethanol towater solvent: 724 nm (FIG. 3A), 656 nm (FIG. 3B), 466 nm (FIG. 3C), and311 nm (FIG. 3D). FIGS. 4A-4D shows histograms of size distribution ofthe iron nanoparticles with different sizes obtained at different ratiosof ethanol to water solvent: 724 nm (FIG. 4A), 656 nm (FIG. 4B), 466 nm(FIG. 4C), and 311 nm (FIG. 4D). The size of iron nanoparticlesdecreased gradually with the increase in the weight ratio of ethanol inthe mixed solvent of ethanol and water. The resulting iron nanoparticleswere highly monodispersed and were well-dispersed in polar solvents suchas water and ethanol.

In summary, monodispersed iron nanoparticles were prepared by chemicalreduction of Fe²⁺ ions in the presence of PVP in aqueous solution and byusing NaBH₄ as reducing agent. The sizes of monodispersed ironnanoparticles can be tuned in the range of 50 nm to 1000 nm bycontrolling reaction conditions.

Example 3 Characterization of the Iron Nanoparticles

X-ray powder diffraction (XRD) (FIGS. 5A-5B), Differential scanningcalorimetry (DSC) (FIG. 6) and Hysteresis loops (FIGS. 7A-7D)characterization were also performed on the iron nanoparticles.

The as-synthesized iron nanoparticles are amorphous, as shown in the XRDmeasurement (FIG. 5A). Iron nanoparticles with high crystallinity can beobtained by annealing the nanoparticles at elevated temperature (e.g.,600° C.) for 3 hours under the protection of nitrogen (FIG. 5B).

DSC was used to measure the crystallization point of amorphous ironnanoparticles. Thermal data were measured at a heating rate of 15° C.min′ under the protection of nitrogen. As shown in FIG. 6, thecrystallization temperature of amorphous iron nanoparticles was around515° C., which was determined by the maximum heat flow peak.

The magnetic properties of iron nanoparticles were characterized bymeasuring the magnetization of these particles as a function of magneticfield. As shown in FIGS. 7A-7D, the magnetization of the ironnanoparticles is as high as 150 emu/g, which is significantly higherthan that of iron oxide nanoparticles (usually below 100 emu/g).Hysteresis loops also indicated that the iron nanoparticles do notretain the magnetic properties when the external field is removed.

As shown in FIGS. 8A and 8B, photographs of the iron nanoparticle sampleshowed that the obtained product is black (FIG. 8A), which indicates thegeneration of pure iron nanoparticles, rather than oxidized Fe₂O₃nanoparticles which are known to be red. The iron nanoparticlesexhibited very strong magnetic properties; they responded to a magnetquickly and moved to the side wall of vials within 1-2 seconds (FIG.8B).

Example 4 Coating the Iron Nanoparticles with Oxides

The surface of iron nanoparticles can be readily coated with oxides ofdifferent compositions. Typical oxides that can be coated include SiO₂,ZrO₂, TiO₂, CuO, Ag₂O, etc. Provided here is an example of coating withsilica oxide. As-prepared iron nanoparticles (55 mg) were dispersed in80 mL ethanol. 20.0 mL of deionized water and 1.0 mL of ammoniumhydroxide solution were added into the dispersion of iron nanoparticles,followed by sonication for 20 minutes. Under vigorous mechanicalstirring (560 rpm), a 0.1 mL of TEOS (tetraethyl orthosilicate) wasadded into the solution at one time. After stirring for 30 minutes,another 0.3 mL of TEOS was added into the reaction. The reactionproceeded at room temperature for 12 hours under continuous mechanicalstirring. The silica-coated iron nanoparticles were collected by using amagnet bar and washed with ethanol and water each for 3 times. Thethickness of silica layer can be controlled by varying the amount ofTEOS added into the reaction. FIG. 9 shows a schematic illustration of arepresentative iron nanoparticle coated with silica and bonding ligands.FIGS. 10A and 10B show SEM images of iron nanoparticles before and afterthe coating with silica shell. FIGS. 11A-11F shows a series ofrepresentative SEM images of iron nanoparticles with a size of about 300nm after being coated with a thin layer of silica. The coating of silicaon iron nanoparticles is further confirmed by TEM imaging of an ironnanoparticle (FIG. 12).

Example 5 Surface Functionalization of Iron Nanoparticles with DifferentOrganic Ligands

A broad range of organic ligands can be directly functionalized on thesurface of iron nanoparticles or through an intermediate layer ofoxides. As an example, after coating the iron nanoparticles with silicashell, acrylate functional groups can be introduced onto the surface ofnanoparticles through silane chemistry as follows. The Si-coated ironnanoparticles were first dispersed in 50 ml ethanol. Subsequently, a 80mg of KH570 (3-mercaptopropyl trimethoxysilane) was added into thesolution. The solution was sonicated for about 15 minutes. Undervigorous mechanical stirring (560 rpm), the reaction proceeded at roomtemperature for 48 hours (covered with Alumina foil). The products werecollected with a magnet bar and washed with ethanol and water each for 3times. The acrylate-functionalized magnetic nanoparticles were dispersedin ethanol for further use.

The presence of silica and KH570 on the surface of iron nanoparticleswas characterized by FT-IR measurement. As shown in FIG. 13, Fe corewith SiO₂ shell nanoparticles nanoparticles exhibit a clear peak ofSi—O—Si (1100 cm⁻¹). The same peak also appears in the samenanoparticles surface-grafted with KH570 molecules. This is confirmed bya C—H Stretch peak located at about 2950-2850 (cm⁻¹) and a C═O peaklocated at 1712-2850 (cm⁻¹).

Example 6 Continuous Synthesis of Iron Nanoparticles in Flow Reactors

A continuous synthetic approach for the production of iron nanoparticlesusing flow reactors was developed and is described here. The reactorscan be fabricated in plastic chips or constructed from tubings. FIG. 14shows a schematic illustration of the setup for continuous synthesis.Two solutions (one solution containing Fe²⁺ and PVP and another solutioncontaining NaBH4 and NaOH) were introduced into a tubing using syringepumps or a pressurized tank. The two solutions were quickly mixed in themixing zone of the reactor and the reaction proceeded to produce ironnanoparticles in the reaction zone. The dispersion of nanoparticles wascollected at the end of the tubing. The size of the iron nanoparticleswas controlled by varying the flow rates of the two solutions and theconcentration of each of the reactants. A simplified setup of thereactor is shown in FIG. 15. A tubing was used as the reactor andreactants were introduced into the tubing and quickly react to produceiron nanoparticles while flowing downstream. By using this approach, wehave produced iron nanoparticles with controllable diameter and narrowsize distribution.

Example 7 Development of Magnetic Iron Nanoparticle-Based DentalAdhesive Resins

A novel adhesive resin doped with iron nanoparticles (FIGS. 16A and 16B)was developed. The adhesive doped with iron nanoparticles can beactively steered, using magnetic forces, to enhance infiltration ofadhesive resin into dentin. To assess the effect of nanoparticleincorporation on kinetic properties of the adhesive, near infraredspectroscopy (NIR) was used to test the degree of conversion (DC) andpolymerization shrinkage stress of the adhesive resin. Severalformulations with various nanoparticle sizes and concentration wereprepared and tested.

As shown in FIGS. 17A and 17B, the DC was influenced by the nanoparticlesize and concentration, but in general, the DC values were comparable tothose described for commercial adhesives. For example, the DC for the900 nm nanoparticle-doped adhesive (5 wt %.) appeared to be comparableto that of the control adhesive without nanoparticles. However, the samenanoparticle-doped adhesive (900 nm, 5 wt %) was associated with smallerpolymerization shrinkage stress than the control (FIG. 17B).

Preliminary experiments were performed to test if the use of shortmagnetic force improves the penetration of the adhesive into dentin anddentinal tubules. Recently extracted human third molar teeth wereobtained and the occlusal third of the crown was removed to exposedentin. The exposed dentin was polished and etched. The prepared teethwere divided randomly into three groups (n=5/group): (1) teeth restoredusing control adhesive (no nanoparticles and no magnetic pull applied);(2) teeth restored using our nanoparticle-doped adhesive (900 nm) and nomagnetic pull; and (3) teeth restored using the nanoparticle-dopedadhesive resin and 60 second magnetic pull. To apply magnetic pull, anoff-the-shelf magnet (1.2 T) was placed directly under the teeth, 25 mmfrom the occlusal surface of the dentin, for 60 seconds while theadhesive was being applied. The adhesive was then cured for 10 secondsand composite resin applied and cured. The teeth were then sectioned toexamine the resin/dentin interface using a scanning electron microscope(SEM). Representative examples are shown in FIGS. 18A-FIG. 18D. Visualinspection of these images revealed that the teeth treated with themagnetic iron nanoparticle-doped adhesive system demonstrated betterpenetration of adhesive resin as evidenced by the denser and longerresin tags. The images also showed evidence of cross-linking betweenresin tags when the novel iron nanoparticle-doped adhesive was used(FIG. 18D). The average depth and the total number of resin tags perfield of view (“density” of resin tags) were quantified in these teeth.It was found that average length and density of resin tags were greaterwhen magnetic pull was applied (FIG. 19A and FIG. 19B). These findingssuggest that the iron nanoparticle-doped adhesive system not onlyincreases the penetration of the adhesive into dentinal tubules, but italso increases the probability that a resin tag forms.

The effect of magnetic nanoparticle-adhesive system on the shear bondstrength of composite resin to dentin was also tested. The teeth wereprepared as described above for SEM examination with one modification: ametal ring was used to control and standardize the area restored withthe composite. The shear bond strength of composite to dentin, using thenovel magnetic nanoparticle adhesive (900 nm), was double that of thecontrols (FIG. 19C). In conclusion, these findings suggest that theincorporation of iron nanoparticles into dental adhesive results insuperior bond strength. The microtensile bond strength, flexuralstrength, and both fatigue strength and fatigue crack growth resistanceof the interface were also tested.

In related studies investigating the biocompatibility of nanoparticlesin dental applications, in vivo experiments were performed to evaluatethe effect of nanoparticles on pro-inflammatory cytokine production inrat teeth.

Experimental cavities in rat mandibular molars were prepared and asterile saline solution was applied containing iron nanoparticles coatedwith polysaccharides (no adhesive was tested). A magnet was used to pullthe iron nanoparticles into the pulp through dentinal tubules. Magneticforces for extended periods (30 min.) were used to test the ability todeliver a large amount of nanoparticles to the pulp. After the deliveryof nanoparticles, the teeth were restored with composite resin and theanimals were allowed to survive for 2, 4 or 24 weeks. Pulpal tissueswere extracted from the teeth after these time points and qRT-PCR wasused to assess the expression of pro-inflammatory cytokines asindicators of pulpal inflammation. Cytokines involved in both the acuteand chronic phases of the immune response including tumor necrosisfactor alpha (TNF-α) and transforming growth factor alpha (TGF-α) werestudied. No significant differences in cytokines were detected in thepulp of teeth treated with these nanoparticles compared to controls(nanoparticles but no pull), and compared to untreated teeth (n=8animals/group, FIG. 20A, p=0.65 and FIG. 20B, p=0.78). These findingssuggest that iron nanoparticles are not detrimental to the pulp. Theeffect of the iron nanoparticle-doped adhesive system on the productionof several pulpal cytokines was tested over a longer follow-up period.The longevity of composite restorations in rat teeth was assessed andhistological examination of pulpal tissues adjacent to compositerestoration were performed.

REFERENCES

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Having now fully described the methods, compounds, and compositionsherein, it will be understood by those of skill in the art that the samecan be performed within a wide and equivalent range of conditions,formulations, and other parameters without affecting the scope of themethods, compounds, and compositions provided herein or any embodimentthereof. All patents, patent applications, and publications cited hereinare fully incorporated by reference herein in their entirety.

1.-22. (canceled)
 23. Iron nanoparticles made by a process comprisingreacting a Fe²⁺ salt with a reducing agent in the presence of a polymersurfactant and a base.
 24. The iron nanoparticles of claim 23, furthercomprising a ligand on the iron nanoparticles.
 25. The ironnanoparticles of claim 24, wherein the ligand is an acrylate.
 26. Theiron nanoparticles of claim 23, further comprising at least one shell onthe nanoparticles.
 27. The iron nanoparticles of claim 26, wherein theat least one shell comprises a metal oxide.
 28. The iron nanoparticlesof claim 26, wherein the at least one shell comprises silica.
 29. Theiron nanoparticles of claim 23, that are embedded in a polymeric matrix.30. The iron nanoparticles of claim 29, wherein the polymeric matrixcomprises a polyacrylate.
 31. The iron nanoparticles of claim 23, linkedto a drug.
 32. A method of treating a condition that responds to a drug,comprising administering an effective amount of the iron nanoparticleslinked to the drug of claim
 31. 33. The iron nanoparticles of claim 23,wherein the iron nanoparticles are part of a dental restoration.
 34. Amethod of treating a condition that benefits from hyperthermia,comprising administering to an animal in need thereof the ironnanoparticles of claim 23, and exposing a portion of the animal to amagnetic field, thereby concentrating the iron nanoparticles to theportion exposed to the magnetic field, and exposing the portion of theanimal to an excitation source, thereby inducing excitation of the ironnanoparticles and localized hyperthermia.
 35. The method of claim 34,wherein the condition is a tumor and the portion of the animal exposedto the magnetic field comprises the tumor.